Glass cloth has been used as an insulative reinforcing material. Generally, the glass cloth is impregnated with a varnish, dried to form a pre-preg, and this pre-preg is then molded to produce a laminated material.
These pre-pregs are usually produced according to a process as illustrated in the flow diagram of FIG. 1. A glass cloth 2 from a roll 1 is introduced into a varnish bath 3, where it is impregnated with a varnish; passed between coaters 4--4, disposed at a set distance apart to remove excess varnish; dried in a drying unit 5; and wound as a pre-preg on roll 6. In order to increase the efficiency of the production of pre-pregs, there has been an increasing trend toward "large packaging" of the roll 1, i.e., the use of a plurality of glass cloth pieces joined together to form a larger continuous glass cloth. Thus, the glass cloth wound on the roll 1 inevitably contains joints or connected portions.
Conventional glass cloth joints are illustrated in FIGS. 2 and 3. In the embodiment of FIG. 2, end portions of the glass cloths 2--2 to be joined together are superposed on each other with a thermoplastic film 7 sandwiched therebetween, and then are joined together by heat-pressing. Alternatively, as shown in FIG. 3, end portions of the glass cloths 2--2 to be joined together are superposed and sewn together with stitching 8. In these joints, however, the thickness of the joint is two or more times the thickness of the glass cloth. This gives rise to some problems in the production of pre-pregs. For example, when these joints pass through the clearance between the coaters 4--4 of FIG. 1, the joint will become caught between the coaters 4--4, unless the clearance is increased, resulting in the tearing of the glass cloth. This problem can be overcome by the provision of an additional mechanism for the opening of the coaters 4--4 when the joint passes therethrough. This, however, requires the provision of more complex equipment. Moreover, if the coaters 4--4 are opened, an excess of varnish attached to that part of the glass cloth which has passed through the clearance while the coaters are opened, and the resulting "sagging" of the varnish causes problems such as attachment of the varnish to guide rollers.